II IE NAUTILUS. 91 



figuration of the aperture with its lamelhe and folds, it stands 

 nearest Bifid. Ashrmini. These two species represent a new type 

 a in 'ing the already very different groups of the genus. 



Bifidaria Dalliana n. >[>. 



Shell minute, ovate-turriculate, perforate-rimate, pale horn-col- 

 ored, translucent; apex somewhat obtuse; whorls 5, regularly in- 

 creasing, convex, with the suture deeper between the upper than the 

 lower whorls ; the last whorl ascending at the aperture, compressed at 

 the periphery, especially so toward the aperture, with a slight, shal- 

 low crest-elevation, its base narrow except just behind the aperture, 

 where there is a slight depression ; surface with very fine, crowded 

 stria;; aperture equaling a little over one-third of altitude, almost 

 as wide as high, rounded below, with three almost equal angles 

 above, margins approximate, somewhat extended upward and con- 

 nected by a slight, straight callus, somewhat everted, especially 

 below, without a thickened lip. Lamella? and folds: angular and 

 parietal rather large, connected but distinct, the former ending at 

 the margin; a nodule-like iufraparietal ; columellar rather large, 

 lamellar, horizontally encircling the somewhat projecting columella ; 

 basal transverse (radial ) on the impressed part of the base, short 

 lamellar, abrupt; parietal folds approximate, the superior rather 

 short, the inferior longer, deeper in the throat, somewhat oblique. 

 Alt. 1.6 to 1.8, diam. 0.8 to 0.9, apert. alt. 0.6 mm. 

 Soft parts very light-colored. Jaw rather strongly arcuate, with 

 rather fine, irregular, crowded, tubercular ribs projecting as irregu- 

 lar denticulations on the cutting edge. Radula 0.48 mm. long, 

 0,13 wide, with 72 transverse rows of 19 teeth, c : 4 : 5 ; the central 

 narrow, with three short cuspids, the laterals bicuspid ; marginals : 

 one tricuspid, the others serrate four to six-cuspid. 

 Habitat. Nogales, Arizona, with the preceding species. 

 Bifid. Dalliana stands near B. hordeacella Pilsbry, for the smallest 

 forms of which it might be mistaken, and some of the smallest West 

 Indian species of the genus. From hordeacella it is distinguished 

 by its being less cylindrical, the presence of the infraparietal nodule, 

 and the basal being lamellar, placed radially upon the impressed 

 part of the base, and nearer the margin than is the basal of hordea- 

 cella. These differences appear to be trifling, but they are signifi- 

 cant. Over thirty lots of B. hordeacella, from Key West, through 

 Florida, Mississippi, Texas, New Mexico, Arizona, and from dif- 



